Same as with any hard drive failure. You reach for the warranty:
Ummm... you do have a backup?
On a conventional hard disk drive, the HDA is not sealed allowing air pressure will slowly equalize. However, with less air inside the HDA, the head flying height is reduced, eventually resulting in a head crash.
According to the ancient Hitachi 15K147 data sheet, 3,048 meters (10,000ft) is the altitude limit.
Presumably, the helium filled HDA assembly will be better sealed, and therefore be better able to withstand high altitudes. However, there is always a possibility of a blow-out or rapid helium loss, which can be easily prevented by having the TSA confiscate all T6 screwdrivers on the flight.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Exotic? Try commodity IBM/Hitachi DeathStar hard disk drives:
Also Toshiba laptop drives:
You can see right through the area where the head has scraped off the plating. Average lifetime was about 2 years.
In the distant past, Parylene was the favored coating. These daze, it's a carbon film that provides the necessary protective layer on the platter.
How do I seal the two halves of the HDA package? Weld them together?
Not all that weird. However, all that would be necessary to prevent entry would be to slightly pressurize the HDA package. It would not prevent leaks, but would prevent external contamination. At this time, all hard disks have an air filter somewhere on the package to allow HDA package pressure to equalize with atmospheric pressure. It's basically a small hole in the cover with a filter. However, that's not going to work with helium because the helium would rapidly leak out through the filter. So, the lid has to be strengthened and the HDA needs to be sealed. The seal design is going to be a challenge.
According to a random Hitachi data sheet, 10,000ft maximum. At low air pressure, the heads don't fly as high, and will crash onto the platter. However, I'm speculating that the helium filled disk drive will need to be sealed, and therefore will retain its pressure at any altitude.
Yep. Then, all Hitachi needs to do is design a package that doesn't change shape at different altitudes and with changes in air pressure. The current hard disks rely heavily on the base plate (bottom of aluminum casting) that supports the motor and head solenoid remaining aligned with each other. The slightest deflection and the head is no longer centered on the track. Disk drives have firmware to help center the head as things drift around (servo tracks or imbedded servo data), but eventually the package might drift out of tolerance and the drive will fail to calibrate when it boots. Allowing a thin metal cover to bulge with changes in air pressure isn't going to work. Stiffening the HDA package will work, but might be difficult. Some kind of sliding piston pressure equalizer might work, but might be too large or leak. Dunno... this is going to be interesting.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Rubber helium balloons are commonly sold here. They last for about a day.
Also, the H2 molecule is hardly larger than a single H atom, and is about the same size as a helium atom.
Cheers
Phil Hobbs
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Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
IBM started selling glass platter HDDs in about 2000. I've disposed of several by cracking the platters with a ball-peen hammer.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Quartz is a pretty good helium barrier, but soda-lime glass isn't. You can kill a soda-lime photomultiplier by putting it in a helium atmosphere for an hour.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Helium filled balloons are usually aluminum coated mylar bags, which are also allegedly self-sealing. I was presented with several during an involuntary visit to the local hospital. When I made my escape, I took them home with me and had a friend re-seal the fill valve with RTV. I would have used my heat sealer if I could have found it.
The balloons lasted about 3 weeks, which is double what I would expect without the RTV re-seal.
Hydrogen diffuses through materials more than helium.
For similar reasons, and also due to the small size of helium atoms, helium's diffusion rate through solids is three times that of air and around 65% that of hydrogen. My guess(tm) is that you had a leak in the He balloon, but that the hydrogen balloon was properly sealed.
More:
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
I was on the task force that was formed to try to figure out what was going wrong with those things--the Desktstar and its server brothers Discovery and Discovery II.
They were the first disk products manufactured by IBM in the Far East, rather than in San Jose, and the overseas guys didn't have the same line discipline as the SJ guys. That debacle was one of the big reasons IBM got out of hard disks in '05.
(My part of the job was using the ISICL particle detector to try to see if there were a lot of particles rattling round in the air inside the disk. I showed that there weren't, which was the sum total of my contribution. Other folks figured out the actual problems, eventually.)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Few recieving tubes were quartz though -- for that matter, few of anything was; I have a Bendix 6384 that uses some sort of hard glass (probably a borosilicate similar to Pyrex) which claims a 200C water quench stress test.
Is it a Le Chatlier effect (not much gets in, even after a century, unless you have ~100% He), or are most tubes just that tolerant of light gasses? Are PMTs overly sensitive to ions?
Speaking of, I don't know what glass hydrogen thyratrons are made of, or how long they store for. You can still find spares and surplus, but I don't know how well they work...
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Borosilicate is a lot better than soda lime, but not as good as quartz.
I think ordinary receiving tubes are a lot more forgiving.
Very much so. An ion can do a couple of nasty things, of which the worst is to accelerate towards the photocathode and crash into it, producing a huge pulse and a bunch of afterpulses.
Hydrogen gets slowed down by chemical reaction with the oxygen in the glass, whereas helium diffusion is pretty much straight kinetics. I have a book on diffusion in solids from when I was trying to design hermetic air-spaced etalons, but I haven't gone through it in any great detail. (And it turned out I could buy the etalons ready-made from Photop anyway.)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Ahhh. And in regular toobs, the secondary emission makes it better if anything (well, probably a lot noisier, but who would notice?) There's enough extra cathode surface that the ionic sandblasting doesn't destroy it too quickly. Ionic wear (sputtering, I suppose) is known, and tends to result in leaky grids; this tends to be a symptom of gassy tubes, oddly enough.
"Cathode stripping" is also known, though it's supposedly an electrostatic, mechanical effect.
The really Good cathodes, made with extremely pure materials, good pumps and careful assembly, made their way into undersea telephone cable repeaters. Among regular tubes, 10k lifetime isn't unheard of, but most power tubes fail in the 2-5k range; these had to last 50k+, first time, guaranteed, and they did.
Huh -- hope the Casimir effect doesn't warp them too much! ;-)
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Huh? There should have been plenty of debris flying around inside the drive after the GMR head gouged its way through the plating. Were you testing before or after a head crash?
Head crashes on aluminum platters are more interesting. I guess(tm) that some people like to hear the screaming sound of the head grinding its way into the platter:
Methinks you would have seen quite a few particles flying around on that head crash.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Before, to try to find out what the root cause was. I screened about half a dozen drives, but didn't find anything out of the ordinary.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
On a sunny day (Sat, 15 Sep 2012 17:36:12 -0700) it happened Jeff Liebermann wrote in :
I worked with these:
formatting link
First ever video slow motion machines from Ampex. head crashed happened all the time, in the end the thing was put in an over-pressure box with air blown in through a micro filter Look at the size! Some spare disk were usually standing next to it in a cardboard box.
4 heads, on steppers... one reading the other one writing and some moving to the next track. Engineering at the peak at that time!
It will. Until it matches the partial pressure of helium in the atmosphere (less than 0.00006 Atm) it will continue to diffuse out. The rate will decrease asymptotically.
atmospheric pressure is probably not enough to crush the disk drive case. Also it's likely that some air will leak in and the plastic parts my emit some hydrocarbons too. this will not effect the rate of helium diffusion.
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It can get back out on its own, just noone wants to leave a multi kilobuck watch in a hypobaric chamber full of nitrogen for a few weeks(?) while the helium escapes.
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